[C1] Knocking Noise
01-19-2019, 09:25 AM
#41
Drifting
This is a diagnostic we used to do for a knock. Bring the rpms up to 2000 and raise and lower the rpms to see if the knock gets a lot more noticeable when backing off and gets quieter as you accelerate, that would indicate a rod knocking. If the sound is loud when the engine is cold and less noticeable when warm then it could be a cracked piston skirt. If the knock is constant, no matter the rpm or engine temp than I would lean toward a loose rocker. Nothing is absolute this can give you a starting point.
01-19-2019, 10:39 AM
#42
Racer
Thread Starter
I took a test drive yesterday to see if the knock would correct with use. I waited until this morning to respond to be sure of the condition would return when cold. I drove calmly until the temp came up and then more briskly as I gained more confidence in the engine. When I was certain the oil temp was up, I made some hits. (2000k to 4000k through the gears). I don’t know exactly when the knocking stopped, because of exhaust noise, but it did and did not return this morning when cold. It may turn loose next time I drive it but for now it seems to be ok. Thanks to all. Jim
01-19-2019, 10:44 AM
#43
Race Director
Wow - not many solid clues to go from in all this!
Heres a real shot in the dark WAG - maybe a carbon deposit that blew out when you exercised it a bit?
Heres a real shot in the dark WAG - maybe a carbon deposit that blew out when you exercised it a bit?
01-19-2019, 10:58 AM
#44
Racer
Thread Starter
Alteady crossed my mind. My carburetor has a tendency to maintain an overly rich condition and keep my spark plugs sooty black. Must make lots of carbon in the cylinders. I just don’t know enough to make an explanation of how it might happen. Jim
01-19-2019, 11:43 AM
#45
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This was the first thing that popped into my head reading the OP's last post just now. Pretty much the only 'knock' that can heal itself!!! Hope it's the case here, and it just may well be.
01-19-2019, 11:55 AM
#46
Team Owner
Some dribble a little water down the carb to de-carbonized things. Several YouTube videos on how to do it. The car will smoke a bit but that’s normal.
I might run some Marvel Mystery oil in the crankcase and fuel system. Pob won’t help but won’t hurt.
I might run some Marvel Mystery oil in the crankcase and fuel system. Pob won’t help but won’t hurt.
Last edited by Frankie the Fink; 01-19-2019 at 01:52 PM.
01-19-2019, 12:16 PM
#47
Race Director
“**** won’t help but won’t hurt” - that’s the funniest spell check mistake I’ve ever seen!
01-19-2019, 12:46 PM
#48
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LOL...I have to agree with that one! WAAAAY better than 'mis-year coolant'!! I personally have done the water-dribble, ATF-MMO dribble a few times over the years, and it does work. GM even had a product specifically for this:Top Cylinder Cleaner. I have a 45 year-old can in the shop!
01-19-2019, 12:48 PM
#49
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Jhemp3 (01-19-2019)
01-19-2019, 01:53 PM
#50
Team Owner
Damn iPhone and my fat fingers. Ugh!
01-20-2019, 09:27 AM
#51
Team Owner
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St. Jude Donor '05
To eliminate the possibility of too much water going down and doing damage a spray bottle with warm water helps. That is one strange sound
If your timing is not real late try a leak down test somewhere if all is good justdrive it. Basically of no use to you lol.
Good luck
If your timing is not real late try a leak down test somewhere if all is good justdrive it. Basically of no use to you lol.
Good luck
01-22-2019, 06:19 PM
#52
Drifting
I took a test drive yesterday to see if the knock would correct with use. I waited until this morning to respond to be sure of the condition would return when cold. I drove calmly until the temp came up and then more briskly as I gained more confidence in the engine. When I was certain the oil temp was up, I made some hits. (2000k to 4000k through the gears). I don’t know exactly when the knocking stopped, because of exhaust noise, but it did and did not return this morning when cold. It may turn loose next time I drive it but for now it seems to be ok. Thanks to all. Jim
01-22-2019, 06:26 PM
#53
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Yep, but the noise did not sound like that at all. And a piston skirt breaking away and falling into the pan is pretty unlikely. Not impossible, but not probable. My 2 cents.....
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Frankie the Fink (01-22-2019)
01-22-2019, 08:02 PM
#54
Racer
Thread Starter
I am pleased that there’s been the number of excellent ideas in the diagnosis of such an elusive engine knock. My decision after considering all comments and running all possible, at least possible by my limited mechanical abilities, diagnoses is to drive, enjoy and repair or replace as appropriate. So far so good. I’ll report if things change. Thanks, guys for the great suggestions. Jim
01-23-2019, 12:59 AM
#55
Le Mans Master
I guess my old ears heard phantom sounds but it sure sounded like a hammer hitting hard on the block inside but without any natural cadence relating to a 4 stroke engine.
Glad you got it running and quiet.
in my experience carbon build up hits every time the piston hits TDC, No randomness at all.
a very random misfire happening unrelated to.fireing order could cause that random heavy misfire detonation I guess, far more feasible than a carbon build up.
Glad you got it running and quiet.
in my experience carbon build up hits every time the piston hits TDC, No randomness at all.
a very random misfire happening unrelated to.fireing order could cause that random heavy misfire detonation I guess, far more feasible than a carbon build up.
